A prior art liquid charging apparatus is disclosed in Facci et al., U.S. Pat. No. 5,893,663 (hereinafter xe2x80x9cFacci Patentxe2x80x9d). An elevational schematic view of the liquid charging apparatus of the Facci Patent is shown in FIG. 1 (which corresponds to FIG. 1 of the Facci Patent). FIG. 1 shows a hydrophilic web 100 wound onto a supply roll 110 and a take-up roll 120. The web 100 is passed over a wetting or moistening device such as a porous roll 130. The porous roll contains a perforated shaft 131 therethrough. A DC voltage 135 is attached to the shaft to provide charge thereto. The DC voltage can be applied to the electrically conductive liquid by a conductive brush, commutator, wire, or similar device. This voltage application contact can occur at a reservoir, delivery tubing, porous roll, central roller or the wetted section of the web. The porous roll 130 uniformly moistens the web 100. As copies are made, the web 100 which is initially wound onto the supply roller 110, is slowly advanced or indexed in a direction (shown by arrow 111) counter to the photoreceptor 10 motion (shown by arrow 16), ensuring that any contamination at the entrance nip 17 is kept to a minimum as it is carried away by the web 100. Also, the contamination is kept out of the nip 18. The charging web 100 is contacted against the photoreceptor 10 by a contact roll 130 which supplies a charging fluid to the web 100 at a controlled rate. The fluid delivery member (or conduit) 51, from the reservoir 140, ensures an even contact pressure across the width of the photoreceptor 10. The width of the contact pad 130 determines the nip width.
In FIG. 1, photoreceptor 10 (which is a drum according to the Facci Patent) contacts the web 100 to result in a tangential contact length. As used herein, the phrase xe2x80x9ccontact lengthxe2x80x9d refers to the distance in the process direction that two surfaces contact. The phrase xe2x80x9cprocess directionxe2x80x9d means the direction of motion of the surface (e.g., photoreceptor) to be charged. The phrase xe2x80x9ctangential contact lengthxe2x80x9d refers to two surfaces that slightly contact one another, that is, where the contact length is short. Besides the tangential contact length depicted in FIG. 1, another illustration of a tangential contact length is if photoreceptor 10 in FIG. 1 were a belt where web 100 contacts the linear surface of photoreceptor 10 to result in a short contact length. A tangential contact length depends for instance on the size of the two contacting surfaces. For purposes of discussion, however, a tangential contact length in the context of a nip formed by the contact of web 100 with photoreceptor 10 (whether photoreceptor 10 has the configuration of a belt, a drum or other conventional shape), is one ranging from 1 mm to 5 mm.
A contact length which is tangential is problematic for a liquid charging apparatus in a electrostatographic printing machine because the tangential contact length may lead to nonuniform charging due to variations in the degree of contact between the the charging apparatus and the surface to be charged. In addition, toner particles stuck under the liquid charging apparatus with a tangential contact length may give rise to nonuniform charging. Thus, there is a need for an improved liquid charging method and apparatus which avoid or minimize the problems discussed above.
Conventional liquid charging devices are also disclosed in Tajima et al., JP 57-49964; Facci et al., U.S. Pat. No. 5,457,523; Lewis et al., U.S. Pat. No. 5,781,833; Facci et al., U.S. Pat. No. 5,895,147; Facci et al., U.S. Pat. No. 5,819,141; and Levy et al., U.S. Pat. No. 5,895,148, the disclosures of which are totally incorporated herein by reference.
The present invention is accomplished in embodiments by providing a method comprising:
(a) dispensing an electrically conductive liquid into a contact member permeable to the liquid;
(b) rubbing the contact member and a surface against each other, at a contact length greater than a tangential contact length, to release the liquid from the contact member to wet the surface with the electrically conductive liquid in a layer ranging in thickness from about 1 to about 100 micrometers; and
(c) electrifying the liquid at any time effective for imparting an electrical charge to the surface.
There is also provided in embodiments an electrostatographic printing machine comprising:
(a) a photoreceptor;
(b) a developer member including toner particles;
(c) a dispensing equipment that dispenses an electrically conductive liquid;
(d) a contact member that receives the liquid and is permeable to the liquid, where the contact member and the photoreceptor rub against each other, at a contact length greater than a tangential contact length, to release the liquid from the contact member to wet the photoreceptor surface with the electrically conductive liquid in a layer ranging in thickness from about 1 to about 100 micrometers; and
(e) a power source that electrifies the liquid.